docs: context directives are enterprise features (#3025)

Add Enterprise feature callouts for context directives

Co-authored-by: Chris Lenfest <clenfest@apollographql.com>

docs/source/entities-advanced.mdx

@@ -918,6 +918,12 @@ This problem is not limited to reference resolvers. In fact, it can occur with a
 
 </MinVersion>
 
+<EnterpriseFeature>
+
+The `@context` and `@fromContext` directives are [Enterprise features](/router/enterprise-features) of the Apollo Router and require an organization with a [GraphOS Enterprise plan](https://www.apollographql.com/pricing/). If your organization doesn't have an Enterprise plan, you can test it out by signing up for a free [Enterprise trial](/graphos/org/plans/#enterprise-trials).
+
+</EnterpriseFeature>
+
 Use the `@context` and `@fromContext` directives to set and get a _context_ to share data between types in a subgraph. Contexts provide a way for a subgraph to share data between types of a nested-type hierarchy without overloading entity keys with extraneous fields. Contexts also preserve the separation of concerns between different subgraphs.  
 
 In an entity, a nested object may have a dependency on an ancestor type and thus need access to that ancestor's field(s).

docs/source/federated-types/federated-directives.mdx

@@ -924,6 +924,8 @@ If different subgraphs use different versions of a directive's corresponding spe
 
 </MinVersion>
 
+<EnterpriseFeature />
+
 The `@context` directive defines a named context from which a field of the annotated type can be passed to a receiver of the context. The receiver must be a field annotated with the `@fromContext` directive. 
 
 ```graphql
@@ -957,6 +959,8 @@ type U @key(fields: "id") {
 
 </MinVersion>
 
+<EnterpriseFeature />
+
 The `@fromContext` directive sets the context from which to receive the value of the annotated field. The context must have been defined with the `@context` directive.
 
 ```graphql